Shotgun cartridge case-sleeve and a cartridge made therefrom

ABSTRACT

Shotgun cartridge cases are disclosed which are produced from a unitary body of plastic material. The shotgun cartridge cases include a cylindrical wall with a based portion which includes a central opening adapted to receive a primer, and a number of grooves extending axially from the end plane of the cartridge case and defining displaceable regions of the base portion whereby these displaceable regions are axially displaceable by means of powder charge gases released by the cartridge. Shotgun cartridges are also disclosed.

FIELD OF THE INVENTION

The present invention relates to shotgun cartridge cases and tocartridges made therefrom.

BACKGROUND OF THE INVENTION

Cartridges for shotgun-shooting have been the subject of heateddiscussions among hunters and shooters for the last century. Theoriesrelating to cartridge action vary from time to time, as do opinions onhow a cartridge case and the components therein should be constructed.

Historically, the development of cartridge cases has progressed frombrass cases, cardboard/metal-base cases, and plastic/metal-base cases tocases manufactured entirely from plastic.

With few exceptions, cases of the latter type have, however, remained onthe drawing board.

The specific requirements for shotgun cartridge cases are particularlydemanding. A utilisable case must be able to tolerate, for example, agas pressure of up to 800 Bar. Its diameter should be such that itcorresponds to nominal gun calibers of ±0.1 to 0.5 mm. After firing, thecartridge case should be easy to remove using an extractor or anejector. Leakage of powder gas should be minimal. The case should beadaptable to all types of shotguns, including semi-automatic shotguns.

Naturally, the case must not rupture or leave residue in the gun, whichcould result in barrel rupture with catastrophic consequences.

The base of the cartridge case serves to form a shape-stable bottom witha seat for the primer. The base also forms the abutment plane againstthe gun's action body.

The case sleeve, particularly its front portion, should create as tighta seal as possible against the bore of the barrel under the influence ofthe gas pressure from the powder charge and the case sleeve should alsobe such that it can accommodate the required components, i. a. powder,wad and shot. The front portion of the case sleeve is advantageouslysuch that it can be upset to thereby create a closure and hold the shotcharge in place against the wad.

As is noted above, attempts have been made to manufacture shotguncartridge cases entirely from plastic. It has been recognized that thematerial costs can thus be reduced and that manufacturing costs can alsobe lower since it allows for rational manufacturing methods.Furthermore, with regard to environmental and recycling aspects, thereare advantages to be gained, particularly if it were possible tomanufacture the shotgun cartridge case solely of a plastic material(mono-material).

One method for manufacturing shotgun cartridge cases of plastic whichhas been used on occasion is based on manufacturing the various parts ofthe cartridge case of mutually separate plastic materials. Thus, for thebase, a stronger, i.e. more pressure-resilient, and more shape-permanentplastic material is selected than that used for the sleeve portion.

One example of this is shown in PCT Application No. WO 86/05871.So-called sequential injection molding is used in the manufacturing ofthe cartridge in which, in a first step, the sleeve portion is injectedand, in connection thereto, in a second step the base portion isinjected using a different plastic material than that of the sleeveportion. Furthermore, in this cartridge construction, the sleeve wall inthe region of the charge and the primer is made so as to consist of twomaterial layers which together provide a stable base.

Another example of manufacturing the base in a separate step using adifferent plastic material than that used for the sleeve body is shownin German Application No. 2,419,577. By a special design of the primerhole with three mutually different diameters, the intention here hasbeen to reduce the risk of powder gas release through the primer hole tothereby reduce the risk of displacement of the primer.

An example of a case sleeve made from biaxially oriented plasticmaterial, in an attempt to reduce the material thickness, is describedin U.S. Pat. No. 5,121,693. The cartridge case in this example isprovided with a traditional base made from metal.

In U.S. Pat. No. 3,760,729 there is disclosed a glass fiber reinforcedplastic cartridge case. The case is explicitly designed to have a rigidbase. There is a groove extending from the end plane of the base portionof the case.

The reasons for having the groove (the term used in the specification ofsaid patent is “coring”) are as follows:

1. to avoid uneven cooling and sinking of the molded case;

2. to avoid long molding cycles required by cooling of the thick base;and

3. to avoid physical weakness at the juncture of the thick base with thethin wall of the case. (See col. 4, lines 1-6).

The plastic cartridge case disclosed in U.S. Pat. No. 3,088,405 is alsodesigned to have a rigid base in the embodiments shown in FIGS. 7,9, and11, and the base of the cartridge is reinforced by a plurality of ribs.In col. 3, starting on line 49 it is stated: “by said ribs 38, tubularsection 34 with counter pocket (probably means “primer pocket”) 35 isinterconnected with the wall of case 31 whereby a firm, rigid structureis provided having adequate support for the primer . . . ”.

A shotgun cartridge case made in one piece from plastic is described inU.S. Pat. No. 3,550,531. According to the disclosure of that patent, thebase portion is designed to be able to optimally convert powder gasenergy into propulsive energy for the shot charge and to prevent thecase from rupturing. The shaping of the base with weakened waistportions between an internal groove and external recesses does, however,imply that there is a large risk of the primer hole expanding such thatpowder gas is forced out between the primer and the wall of its hole.The primer can be displaced from its position and make it impossible tobreak the gun after firing.

It is therefore an object of the present invention to provide a shotguncartridge case made completely of plastic, and shotgun cartridges madetherefrom, in which the cartridge case is made in one piece by injectionmolding of a single plastic material (mono-material), and in which thebase portion is shaped so that it meets current specification demandsand functions at least as well as a traditional metal base.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other objects havenow been realized by the invention of a shotgun cartridge casecomprising a unitary body of plastic material including a cylindricalwall having an outer surface and an inner surface and a base portiondefining an end plane and having an inner wall, the base portionincluding a central opening adapted to receive a primer, and a pluralityof grooves extending axially from the end plane and defining a pluralityof displaceable regions of the base portion, whereby the displaceableregions of the base portion are axially displaceable by means of powdercharge gases released by the cartridge. Preferably, the plurality ofgrooves extend through a substantial portion of the base portion.

In accordance with one embodiment of the shotgun cartridge case of thepresent invention, the plurality of grooves includes a first groovecomprising an inner circular groove proximate to the central openingthereby defining an inner material portion of the base portion betweenthe first groove and the central opening and a second groove comprisingan outer circular groove distal to the central opening thereby definingan outer material portion of the base portion between the second grooveand the outer surface of the cylindrical wall. Preferably, the shotguncartridge case includes an extractor rim extending radially outwardlyfrom the outer material portion adjacent to the end plane.

In accordance with one embodiment of the shotgun cartridge case of thepresent invention, the case includes a plurality of third groovesextending radially within the base portion between the first groove andthe second groove. In a preferred embodiment, the plurality of thirdgrooves are equidistantly spaced from each other, whereby each of theplurality of displaceable regions of the base portion is formed by apair of the third grooves, the first groove and the second groove.

In accordance with another embodiment of the shotgun cartridge case ofthe present invention, the case includes a plurality of radial innerwebs and a plurality of radial outer webs, each of the plurality ofdisplaceable regions being connected to the inner material portion andthe outer material portion by at least one of the plurality of radialinner webs and at least one of the plurality of radial outer webs. In apreferred embodiment, the plurality of radial inner webs and theplurality of radial outer webs has a first thickness and the pluralityof displaceable regions has a second thickness, the first thicknessbeing substantially less than the second thickness. Preferably, theouter material portion and the inner material portion include an axialend surface, and the plurality of displaceable regions include axial endsurfaces, and the axial end surfaces of the outer material portion, theinner material portion, and the plurality of displaceable regions aresubstantially planar and lie in a common radial plane.

In accordance with another embodiment of the shotgun cartridge case ofthe present invention, the base portion includes a maximum axialthickness and the plurality of grooves extend through the base portion adistance at least about two-thirds of the maximum axial thickness. In apreferred embodiment, the case includes a transition wall regionconnecting the inner wall of the base portion to the inner wall of thecylindrical wall, the transition wall region having a varying wallthickness whereby a conically tapering charge combustion chamber isprovided facing the central opening.

In accordance with another embodiment of the shotgun cartridge case ofthe present invention, the inner material portion has a first radialthickness and the outer material portion has a second radial thickness,the first radial thickness being substantially greater than the secondmaterial thickness. In a preferred embodiment, the first radialthickness is at least two times the second radial thickness.

In accordance with another embodiment of the shotgun cartridge case ofthe present invention, the first groove has a first depth defining afirst base wall and the second groove has a second depth defining asecond base wall, the second depth being greater than the first depthwhereby a line connecting the first base wall to the second base wallhas a curvature substantially corresponding to the inner wall of thebase portion, whereby the axial displacement of the plurality ofdisplaceable regions is facilitated.

In accordance with another embodiment of the shotgun cartridge case ofthe present invention, the central opening in the base portion includesa first portion adjacent to the end plane having a first width and asecond portion adjacent to the inner wall of the base portion having asecond width, the second width being greater than the first width. In apreferred embodiment, the second width of the central opening defines anenlarged cylindrical surface in the central opening.

In accordance with another embodiment of the shotgun cartridge case ofthe present invention, the first portion of the central opening and thesecond portion of the central opening have substantially the same axiallength.

In accordance with the present invention, a shotgun cartridge has alsobeen invented comprising a unitary body of plastic material including acylindrical wall having an outer surface, an inner surface, a first endand a second end, and a base portion at the first end of the cylindricalwall defining an end plane and having an inner wall, the base portionincluding a central opening adapted to receive a primer, the cartridgeincluding an end closure at the second end of the cylindrical wall, awad member disposed within the cartridge and spaced from the end closureand the base portion whereby the space between the end closure and thewad member is adapted to receive shot means and the space between thewad member and the base portion is adapted to receive a powder charge,and a plurality of grooves extending axially from the end plane anddefining a plurality of displaceable regions of the base portion,whereby the plurality of displaceable regions of the base portion areaxially displaceable by means of the powder charge gases released by thecartridge.

In accordance with a preferred embodiment of the shotgun cartridge ofthe present invention, the cartridge includes the primer disposed in thecentral opening, the primer including an outer surface for contactingthe inner surface of the central opening, the outer surface of theprimer including a pattern of recessed means.

In accordance with another embodiment of the shotgun cartridge of thepresent invention, the central opening in the base portion includes afirst portion adjacent to the end plane having a first width and asecond portion adjacent to the inner wall of the base portion having asecond width, the second width being greater than the first width.Preferably, the cartridge includes adhesive means disposed within thesecond portion of the central opening for adhering the primer to thecentral opening. In a preferred embodiment, the second width of thecentral opening defines an enlarged cylindrical surface in the centralopening.

In accordance with another embodiment of the shotgun cartridge of thepresent invention, the first portion of the central opening and thesecond portion of the central opening have substantially the same axiallength.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood by referring tothe following detailed description which, in turn, refers to theattached drawings, in which:

FIG. 1 is a side, elevational, cross-sectional view of a shotguncartridge case according to a preferred embodiment of the presentinvention;

FIG. 2 is a partial, side, elevational, cross-sectional, enlarged viewof the case shown in FIG. 1;

FIG. 3 is a bottom, elevational, plan view of the base portion of thecase shown in FIG. 1;

FIG. 4 is a side, elevational, cross-sectional view of the case in FIG.1 in a sealed and charged condition with its constituent componentstherein;

FIG. 5 is a side, elevational view of a shotgun cartridge case beforeits front portion is upset;

FIG. 6 is a side, elevational, cross-sectional view of a shotguncartridge with an arrangement for ensuring the location of the primer;

FIG. 7 is a partial, side, elevational, cross-sectional, enlarged viewshowing the base portion with the primer hole according to oneembodiment of the present invention;

FIG. 8 is a partial, side, elevational, cross-sectional, enlarged viewof the base portion with the primer hole and associated base parts in amodified embodiment of the present invention;

FIG. 9 is a schematic, side, elevational view of the primer withassociated adhesion-increasing means removed from the seat in the baseof either of the embodiments in FIGS. 7 and 8 hereof; and

FIG. 10 is a partial, side, elevational, cross-sectional, enlarged viewof another embodiment of a shotgun cartridge case according to thepresent invention.

DETAILED DESCRIPTION

The shotgun cartridge case shown in FIG. 1 is manufactured in one pieceby the injection molding of plastic material. In a preferred embodiment,the material is HD-polyethylene. The injection molding takes place in amulti-stage tool which is provided with means for core drawing or thelike in order to make shaping as simple as possible. Measures have beentaken in the mold to counteract shrinking of the plastic material,though at the same time this is done so that optimal materialthicknesses can be used throughout the final product. The materialthicknesses in question are, for example, cartridge case sleeve withabout 1 to 2 mm thickness and the base portion in the axial directionbeing about 5 to 8 mm.

The cartridge case comprises a sleeve having a cylindrical wall 10 and abase portion 11 having an opening 12 intended to receive a primer.

The base portion 11 is provided with a pattern of grooves, i.e. an innercircular groove 13 around the primer hole 12 and a radially outercircular groove 14. Radial grooves 15 are connected to these circulargrooves at peripherally equidistant distances. All of these groovesextend relatively deeply into the base portion from its end plane 16 andthus present considerable extensions in the axial direction of thecartridge case. The depth of the grooves in a preferred embodimentextends to at least ⅔ of the material thickness of the base portion 11,as represented by the distance between the dashed lines 16 and 17 inFIG. 1. Heels 18 are formed between the grooves, 13, 14 and 15, and arelocated peripherally equidistant from each other in the base portion 11.

The grooves, 13 and 14, in FIG. 1 have been shown as having the samedepth, though it is also possible to provide the grooves with differentdepths, as shown in FIG. 10, so that the outer groove 14 extendssomewhat further into the material in the base portion, to the levelindicated by 19.

A first circumferentially extending material portion 20 is situatedbetween the inner circular groove 13 and the primer hole 12, and thismaterial portion has a radial material thickness which is greater thanthe radial material thickness of a radially outer material portion 21which is delimited by the outer groove 14.

A seat 22 is formed in the end surface of the first material portion 20for the rim of the primer. The hole 12 is dimensioned so that the primercan be fixedly held by the walls of the hole with a press fit. Theradially outer material portion 21 terminates in an extractor rim 23.The material thickness in the radial direction of the circumferentialmaterial portion 20, as previously mentioned, is considerably thickerthan the corresponding material thickness of the radially outer materialportion 21. The purpose of the inner material portion 20 is to retainthe primer in its proper place during the formation of powder gas and,for this purpose, the greatest possible radial material thickness shouldbe used for the inner material portion 20. At the same time, thematerial thickness in the radial direction must not be too small for theouter circumferential material portion 21 since the extractor rim 23must provide the necessary abutment strength for the gun's extractorafter firing. Trials have shown that a ratio of at least about 2:1between the material thicknesses of the inner material portion and theouter material portion is desirable.

A circular waist portion 25 of reduced material thickness remainsbetween the heels 18 and the powder charge base 24 between the dashedlines, 26 and 27 (FIG. 2). As a result of the particular symmetricalplacement of the heels 18 and the sizing of the material thickness ofthe waist 25, as well as the material thickness in the given manner ofthe inner material portion 20, preconditions have been attained forcontrolled absorption of the gas pressure with retention of the primerin its proper location in the hole 12.

The placement and guiding of the heels, both during manufacturing andduring use, are further aided by arranging material webs, 28 and 29,with an axial length somewhat shorter than the depth of the groove inthe shown embodiment, radially in respective groups, 13 and 14, and madein one piece with both the heels and the material portions, 20 and 21.The purpose of these webs, which have considerably less materialthickness in the peripheral direction than the heels 18, is to stiffenthe base portion, though still permitting the heels to perform theirintended function. As a result of this dimensioning and placement of thematerial portions, the grooves, the heels and the webs, as well as thestated material thickness dimensioning, the embodiment of the baseportion of the shotgun cartridge case shown in FIGS. 1-3 is particularlysuited to tolerate the high gas pressure which arises during firing.

The gas pressure follows the law of least resistance and since thecircumferential waist 25 and the heels 18 formed in one piece therewithis the weakest region seen from the powder charge, this will provide atranslatory force acting axially towards the powder base 24 whichelastically projects the heels 18 a short distance away from the bottomplane 16. The strain on the walls of the primer hole 12 will be minimalfrom this translatory force and the primer will be maintained in itsengagement position against the walls of the hole.

The outer wall of the primer can also be provided with a suitablepattern of recesses, grooves or knurling.

When the primer is being press-fitted into the primer hole, the plasticmaterial is enabled to “flow out” and form a friction-increasingarrangement with the pattern of recesses. In certain cases, and aspreviously mentioned, it can be advantageous to make the outer groove 14deeper. This can be particularly advantageous when the powder combustionchamber has the curvature as shown in the drawing, whereby the materialthickness in the waist 25 becomes more uniform along its entire radialwidth.

A shotgun cartridge case is shown in FIG. 4 according to theabove-described embodiment, in a loaded condition. In the shown example,a top closure has been attained by upsetting the sleeve end 30 shown inFIG. 5. The upset end is placed above the shot charge 31 which isaccommodated in a bowl of a known type of wad 32 which is provided witha bottom bowl to define a powder chamber 33 between the wad and the baseportion of the case. A primer 34 is located in the primer hole 20.

Since the subject of the present invention, including the primer, is amass-produced product, every change to constituent standard componentsnaturally implies an increase in the cost of the end product. In certainapplications, it is not justifiable to manufacture particular primers orsubsequently machine standard primers, and there is thus a need for amore cost-effective solution to the problem of further securing theprimer against displacement and leakage of powder gases.

Examples of such solutions are shown in FIGS. 6-9. In FIG. 6, a seat 22for the rim of the primer is formed in the end surface of the baseportion. The size of the hole 12 is such that the primer is insertable,preferably by a press fit, in the hole 12. At the end of the primer hole12 facing the powder chamber 33, there is provided a circumferentialwidening 35, in the example in the form of an enlarged cylindricalportion of the primer hole 12 in the base portion. The extension in theaxial direction for the enlarged cylindrical portion 35 is, in thisembodiment, about half the length of the hole 12 which forms the openingfor the primer 34.

In FIG. 7, the arrangement of the widening 35 of the primer hole 12 isshown on a larger scale. The dashed lines 36 denote the extension of thehole 12 without the widening. Once a primer has been inserted, thewidening 35 forms a distinct, well defined space in the base portion 11between the outside of the primer and the delimiting side of thewidening, i.e. concentric cylindrical sides defining a shaped cavity 37in the shown example.

The shaped cavity 37 is intended to accommodate means which provideadhesion at least to the outside of the primer 34. As is known, theprimer is made from metal, while the cartridge case is entirelymanufactured from a monoplastic, for example HD-polyethylene. Means forachieving adhesion are present in many forms, including flowing forms.The choice of a suitable adhesion means/adhesive is made by initiallytaking into account its ability to achieve binding with the primer ofmetal, whereby this binding should be as strong as possible. Certainadhesion to the plastic in the base portion is of course advantageous ifthis can be achieved. The purpose of the adhesion-creating means in theshaped cavity or the gap 37 is to provide the primer with a peripheralcollar 38 as shown in FIG. 9. This collar 38 is attained by injecting aliquid binder into the shaped cavity or the gap 37 after application ofthe primer in a conventional manner in the base portion 11 so that thebinder hardens and forms the collar 38.

In order to attain the widening of the primer hole according to FIG. 7,the cylindrical primer hole 12 is suitably bored out to a depthcorresponding to approximately half the material thickness, whereby theboring determines the delimiting wall of the widening 35. Alternatively,the special hole shaping can take place directly in connection with theinjection molding, though this demands further measures when removingthe cartridge case from the mold.

Since the means which create adhesion are preferably very fluid, acertain quantity of this means can seep into the region of the primerhole which is normally dimensioned to be a press fit against the primer.This can further improve locating of the primer.

Primarily, however, locating will be achieved with the collar 38, i.e.increase with a radial width of the shaped cavity, whereby the adhesionof the collar 38 to the primer will also determine the locating orretaining capability.

Even though only one type of widening for forming a collar has beenshown, it will be realized that other shapes than the cylindrical shapeare applicable even if, from a production point of view, cylindrical ispresently optimal.

The adhesive means can also be applied so that the collar 38 at the topof FIG. 9 is given a peripheral brim which is entirely or partiallyadhesively fastened to the bottom of the powder chamber and formsfurther reinforcement of the fastening of the primer.

The described embodiments of the shotgun cartridge cases and cartridgeshereof are presently the most preferred, though it is to be realizedthat there are possibilities of variation of the groove pattern in thebase portion, though the basic idea is that the grooves will provide atranslatory displacement of weakened regions in the base portion withoutthe position of the primer being affected. In addition, the energy whichis consumed when executing the translatory displacement will favorablycontribute to reducing the stresses in the transition region between thebase portion and the cartridge case sleeve, thereby avoiding rupture.

Even though mono-plastic material has been mentioned in the description,it is to be understood that it does not necessarily have to be a “pureplastic material”. Instead, additions of fillers, for example chalk orthe like, can be suitable if such material can otherwise fulfil therequired demands.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

What is claimed is:
 1. A shotgun cartridge case comprising a body including a cylindrical wall having an outer surface and an inner surface and a base portion defining an end plane and having an inner wall, said entire cartridge case comprising a unitary one-piece body of plastic material, said base portion including a central opening adapted to receive a primer, and a plurality of grooves extending axially from said end plane, said plurality of grooves including radial groove means and circumferential groove means defining a plurality of displaceable regions of said base portion defined by both said radial groove means and said circumferential groove means, whereby said displaceable regions of said base portion are axially displaceable by means of powder charge gases released by said cartridge.
 2. The shotgun cartridge case of claim 1 wherein said plurality of grooves extend through a substantial portion of said base portion.
 3. The shotgun cartridge case of claim 1 wherein said circumferential groove means includes a first groove comprising an inner circular groove proximate to said central opening thereby defining an inner material portion of said base portion between said first groove and said central opening and a second groove comprising an outer circular groove distal to said central opening thereby defining an outer material portion of said base portion between said second groove and said outer surface of said cylindrical wall.
 4. The shotgun cartridge case of claim 3 including an extractor rim extending radially outwardly from said outer material portion adjacent to said end plane.
 5. The shotgun cartridge case of claim 3 wherein said radial groove means comprises a plurality of third grooves extending radially within said base portion between said first groove and said second groove.
 6. The shotgun cartridge case of claim 5 wherein said plurality of third grooves are equidistantly spaced from each other, whereby each of said plurality of displaceable regions of said base portion is formed by a pair of said third grooves, said first groove and said second groove.
 7. The shotgun cartridge case of claim 6 including a plurality of radial inner webs and a plurality of radial outer webs, each of said plurality of displaceable regions being connected to said inner material portion and said outer material portion by at least one of said plurality of radial inner webs and at least one of said plurality of radial outer webs.
 8. The shotgun cartridge case of claim 7 wherein said plurality of radial inner webs and said plurality of radial outer webs has a first thickness and said plurality of displaceable regions has a second thickness, said first thickness being substantially less than said second thickness.
 9. The shotgun cartridge case of claim 8 wherein said outer material portion and said inner material portion include an axial end surface, and said plurality of displaceable regions include axial end surfaces, and wherein said axial end surfaces of said outer material portion, said inner material portion, and said plurality of displaceable regions are substantially planar and lie in a common radial plane.
 10. The shotgun cartridge case of claim 1 wherein said base portion includes a maximum axial thickness and said plurality of grooves extend through said base portion a distance at least about two-thirds of said maximum axial thickness.
 11. The shotgun cartridge case of claim 10 including a transition wall region connecting said inner wall of said base portion to said inner wall of said cylindrical wall, said transition wall region having a varying wall thickness whereby a conically tapering charge combustion chamber is provided facing said central opening.
 12. The shotgun cartridge case of claim 3 wherein said inner material portion has a first radial thickness and said outer material portion has a second radial thickness, said first radial thickness being substantially greater than said second material thickness.
 13. The shotgun cartridge case of claim 12 wherein said first radial thickness is at least two times said second radial thickness.
 14. The shotgun cartridge case of claim 12 wherein said first groove has a first depth defining a first base wall and said second groove has a second depth defining a second base wall, said second depth being greater than said first depth whereby a line connecting said first base wall to said second base wall has a curvature substantially corresponding to said inner wall of said base portion, whereby said axial displacement of said plurality of displaceable regions is facilitated.
 15. The shotgun cartridge case of claim 1 wherein said central opening in said base portion includes a first portion adjacent to said end plane having a first width and a second portion adjacent to said inner wall of said base portion having a second width, said second width being greater than said first width.
 16. The shotgun cartridge case of claim 15 wherein said second width of said central opening defines an enlarged cylindrical surface in said central opening.
 17. The shotgun cartridge case of claim 15 wherein said first portion of said central opening and said second portion of said central opening have substantially the same axial length.
 18. A shotgun cartridge comprising a body including a cylindrical wall having an outer surface, an inner surface, a first end and a second end, and a base portion at said first end of said cylindrical wall defining an end plane and having an inner wall, said entire cartridge case comprising a unitary one-piece body of plastic material, said base portion including a central opening adapted to receive a primer, said cartridge including an end closure at said second end of said cylindrical wall, a wad member disposed within said cartridge and spaced from said end closure and said base portion whereby the space between said end closure and said wad member is adapted to receive shot means and the space between said wad member and said base portion is adapted to receive a powder charge, and a plurality of grooves extending axially from said end plane, said plurality of grooves including radial groove means and circumferential groove means defining a plurality of displaceable regions of said base portion defined by both said radial groove means and said circumferential groove means, whereby said plurality of displaceable regions of said base portion are axially displaceable by means of the powder charge gases released by said cartridge.
 19. The shotgun cartridge of claim 18 including said primer disposed in said central opening, said primer including an outer surface for contacting the inner surface of said central opening.
 20. The shotgun cartridge of claim 18 wherein said central opening in said base portion includes a first portion adjacent to said end plane having a first width and a second portion adjacent to said inner wall of said base portion having a second width, said second width being greater than said first width.
 21. The shotgun cartridge of claim 20 including adhesive means disposed within said second portion of said central opening for adhering said primer to said central opening.
 22. The shotgun cartridge of claim 21 wherein said second width of said central opening defines an enlarged cylindrical surface in said central opening.
 23. The shotgun cartridge of claim 21 wherein said first portion of said central opening and said second portion of said central opening have substantially the same axial length. 